It is known that an internal combustion engine installed in an automotive vehicle has a variety of devices for ensuring proper operating performance. For example, it typically includes a fuel jet device for supplying a jet of fuel to the engine, an idling-up device for adjusting the number of revolutions to a slightly higher than normal setting during idling in order to stabilize the idling motion in the engine, and an EGR mechanism for reducing NOx contained in the exhaust fumes. These devices are typically controlled by a controller (control circuit) such as a microcomputer.
Such controller installed in an engine for controlling various devices is disclosed, for example, in the Japanese Laid-open Patent Sho No. 60-219432. What is shown in this publication contains, within the controller, a computer for controlling the motor of the idle speed adjusting device and actuators of other devices, and a dignosis circuit for supporting the action in the event of failure of the computer. This computer in the controller turns on the main relay for the controller when the ignition switch is turned on to supply electric power, and controls to operate the motor and actuator according to an incorporated program, and initializes the motor and actuator and turns off the main relay when the ignition switch is turned off. The diagnosis circuit in the controller is intended to avoid the risk of unexpected onset of accident if the computer goes wrong, and the main relay is not turned off when the ignition switch is turned off, and the power source is continuously supplied, and the motor and actuator are not initialized. In such a case, this diagnosis circuit securely turns off the main relay when the ignition switch is turned off to shut off power supply to the controller, thereby initializing the motor and actuator, so that secure control is guaranteed.
The controller disclosed in this cited publication controls various devices according to an incorporated program. However, as the program for controlling the engine, if there are two programs, for example, program A not considering the action of an engine auxiliary unit such as EGR mechanism, and program B considering the action of EGR mechanism (the inputs and outputs other than EGR are common, and the action logics are separate), individual controllers are necessary for programs A and B, and therefore when assembling the controller into the engine, the control becomes very complicated. Besides, considering the possibility of mismatching of the controllers, diagnostic detection means for detecting wrong matching is needed in each controller, and if this means is not provided, mismatching may lead to worsening of emission.
A primary object of the present invention is to provide a diagnosis arrangement for a vehicle engine controller in which the action of an auxiliary engine control system, which includes an arrangement controlled by a control program selected from a plurality of control programs stored therein, is inspected based on a check signal taken therefrom, to see whether it is operating in a manner corresponding to the selected control program.